IT212, How Computers Work InputOutput

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IT-212, How Computers WorkInput/Output

• Electrical and Computer Engineering
• Spring 2001

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History of I/O Devices
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Analog vs. Digital

• Analog
• Continuous
• Time
• Every time has a value associated with it, not
  just some times
• Magnitude
• A variable can take on any value within a range
• e.g.
• Temperature, voltage, current, weight, length,
  brightness, color

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Quantization

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Analog vs. Digital

• Digital
• Discontinuous
• Time (discretized)
• The variable is only defined at certain times
• Magnitude (quantized)
• The variable can only take on values from a
  finite set
• e.g.
• Switch position, digital logic, Dow-Jones
  Industrial, lottery, batting-average

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A to D to A Process
Digital data is processed by CPU, sounds are
interpreted as spoken words. Another program
then converts these words into how the computer
would pronounce these words (in binary).
Sound causes sensor within microphone to vibrate,
changing output voltage
These binary codes must be converted into analog
voltages which will cause membranes in the
speaker to vibrate (using digital to analog
conversion)
These output voltages must be converted to
digital values (using an analog to digital
converter)
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Analog to Digital

• A Continuous Signal Is Sampled at Intervals and
  Converted to a Quantized Representation of Its
  Magnitude at That Time
• Samples are usually taken at regular intervals
  and controlled by a clock signal
• The magnitude of the signal is stored as a
  sequence of binary valued (0,1) bits according to
  some encoding scheme

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Digital to Analog

• A Binary Valued, B 0, 1 , Code Word Can Be
  Converted to Its Analog Value
• Output of D/A Usually Passed Through Analog Low
  Pass Filter to Approximate a Continuous Signal
• Many Applications Construct a Signal Digitally
  and Then D/A
• e.g., RF Transmitters, Signal Generators

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Why Digital?

• Increased Noise Immunity
• Reliable
• Inexpensive
• Programmable
• Easy to Compute Nonlinear Functions
• Reproducible
• Small

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Digital Cameras
After picture is taken, charge is transferred
along a string of photo cells, until it reaches
charge detection device
Filters prevent all but red light from reaching
these photocells
Digital Camera
Two dimensional area
Each photocell stores charge based upon the
intensity of filtered light which strikes it
ADC
ADC
ADC
Charge Coupled Device (CCD)
Digitized Data
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Supply Current Problems
Normal
VoltageSurge
VoltageDrop (brownout)
Additive Noise
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Surge Protectors

• Prevent Damage/Improper Operation Electronic
  Components Due to Large Voltage Spikes Which Can
  Be Caused By
• High power motors electrically nearby
• Switching of power by utility company
• Lightning

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Typical components

• Metal Oxide Varistor (MOV)
• Shunts current when voltage is above threshold
• Threshold set substantially above normal voltage
• Thermal Fuse
• Low value series resistor
• If current is too high, resistor melts, breaking
  path
• Once melted, protector cannot be repaired
• Toroidal Choke Coil
• Inductor which has high resistance to sudden
  changes in current

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UPS

• Uninterruptible Power Supply
• Unexpected Loss of Power to PC Causes Loss of
  Volatile Data
• Types
• On-Line Continuous
• Off-Line Change over
• UPS senses loss of line voltage and creates
  replacement line voltage to PC

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Uninterruptible Power Supplies
Rectifier (battery Charger)
When A/C power goes off, battery still delivers
charge for at least 5 minutes
Inverter
To Computer
Online (serial) UPS
Offline (passive) UPS
To Computer
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Buses

• Provides Means for Data, and Power to Be
  Distributed Among Various Components
• Traces (wires) in and on circuit board
• Contacts
• Slots
• Communications protocol
• Buses Provide Flexibility in Adding/removing
  Components

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Expansion bus

• ISA Industry Standard Architecture
• Low-speed, 8 MHz
• Used for serial, parallel, internal modems
• 8/16-bit parallel data transfer
• SCSI Small Computer System Interface
• High-speed peripherals, 5 to 20 MHz
• 8/16-bit parallel data transfer

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Local Bus

• Direct Connection to CPU
• High Speed Applications, e.g., Video
• PCI Peripheral Component Interconnect
• AGP Advanced Graphics Port

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PCI

• Slot Not Port
• Dominant Interface Today
• 32 Bits of Data in Parallel Transfer
• High Speed Applications
• Video
• Network Interface Card (NIC)
• Disk
• 132 MB/sec

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AGP

• Slot Not Port
• Prime Graphics Interface for New PCs
• Performance Options (1x, 2x, 4x)
• Dual Row of Connectors (Two Horizontal Lines)
• Based Upon PCI Development
• Designed for CPU to Graphics Only
• 1,066 MB/sec (4x Mode)

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Interfacing to High-end CPUs
Direct memory access (DMA) video devices can
access RAM without bothering CPU
All I/O requests from CPU (both local and
non-local are sent to AGP chip set
Pentium III
32-bit, 33 MHz
32-bit66 MHz
AGP chip set
32-bit33 MHz
32-bit33 MHz
16-bit, 8 MHz
32-bit33 MHz
AGP slot
ISA Slots
PCI Slots
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Computer Ports

• Connect PC to External Devices
• Parallel printer, zip drives, SCSI emulator
• Serial modem
• USB
• EIDE
• SCSI

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Parallel Port Protocol

• Printer Asserts Line 13 to Indicate It Is Ready
  for Data
• PC Outputs Data to Lines 2 Through 9
• PC Pulses Line 1 for 1 ?second Indicating to
  Printer That Data Is Ready
• Printer Asserts Line 11 Indicating That It Is
  Busy
• Reading data, buffer full, paper jam, etc.
• Printer Asserts Line 10 Acknowledging Receipt of
  Byte

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Other Parallel Port Lines

• Line 12 Printer Out of Paper
• Line 15 Unspecified Printer Error
• Line 16 PC Reset Signal to Printer
• Line 14 PC Asserts to Indicate that Paper Should
  Automatically Advance With Carriage Return
• Line 17 PC Asserts to Stop Printer From
  Accepting Data (Rarely Used)

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Serial Port
PC
Telephone
Modem
Data Terminal Equipment (DTE)
Data Communications Equipment (DCE)
Ma Bell
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Serial Port Physical Connection

• Variety of Connectors at Both Ends of Cables of
  Different Sizes
• 9-pin vice 25 pin connector and cable
• Adapters
• Not all pins always connected
• Port/Modem pin numbers not same at both ends
• DTE Data Terminal Equipment
• DCE Data Communications Equipment
• Null Modem for DTE to DTE (PC to PC)

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Serial Port Protocol

• Pin 6 is same at both endsindicates data is
  ready to be sent.
• Pin 4 on PC indicates to pin 20 on Modem that It
  Is Ready to send Data From the PC
• Pin 7 on PC connects to pin 4 on Modem. Modem
  sends a signal indicating it is ready to receive
  data.
• Pin 8 on PC sends a signal to MODEMs Pin 5 When
  It Is Ready to Receive Data from Modem.
• Pin 2 PC Sends One Data Bit to MODEMs Pin 3
• Pin 3 PC Recieves One Data Bit from MODEMs Pin 2
  
• Pin 9 on Pc connects to MODEMs Pin 22 to
  Indicate Telephone Ring

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Universal Serial Bus (USB)

• Interface between the hardware and software.
• Serial Port Supports Only Single Connection
  Between Two Devices
• Cable can be attached to another USB Hub in order
  to provide more USB connections.
• Support connections to every type of external
  peripheral. (monitor, keyboard, printer, etc)

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Serial Port
Pin no 2 3 4 5 6 7 8 9
Pin no 3 2 20 5 6 4 5 22
Data send from PC (1bit)
Data send from Modem (1bit)
Pc Works properly to receive data
Data ready
Modem ready to receive data
PC ready to receive data
PC detect a phone ring
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Universal Serial Bus (USB)
PC
USB Controller
Host Hub
Downstream
Function Hub
Hub
Function
Can handle up to 127 devices
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USB

• Initial Connection
• 4 wire in which two supply electrical power to
  the peripheral.
• Two other lines uses D/D- to send data and
  commands. DHV (1) D-HV (0)
• USB Device identifies itself to USB host
  controller
• D (HV) means the device is high speed (12
  MB/sec). Used for monitors, scanners and
  printers.
• D- (HV) slower data transfer (1.5 MB/sec). Used
  for keyboard and mouse.
• Assigns ID number
• send/receive requirements

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USB

• Once every ?second, host controller broadcasts
  commands
• Host message provide token to indicate the
  peripheral to which message send to
• Device that do not match token address ignore the
  command.
• Host controller must give permission before
  device can put its data on bus

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USB Data Transfer types

• Three types of data transfer
• Isochronous (real time)
• No interruption allowed (e.g., video stream)
• Interrupt Transfer
• Device issues occasional interrupt to get
  processors attention (e.g., keyboard)
• Bulk Transfers
• Much data, much time (e.g., printer)

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EIDE (Enhanced Integrated Device Electronics)

• Early PCs Required Hard Drive Specifics (Sector
  Size, Number of Tracks, etc.) in BIOS
• Enhanced Integrated Drive Electronics
• All interface electronics in drive
• PC sees generic drive
• 2 EIDE interfaces typically built into
  motherboard
• Each EIDE slot can feed two devices
• Master/slave identified by jumpers on drive
• Hard drive, floppy drive, CD-ROM, tape
• Connected via 40-wire ribbon cable

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SCSI (Small Computer System Interface)